CBSE Class 9 Science Chapter 08 Journey Inside The Atom MCQs Set 03

Science Objective Questions and Answers: Chapter 08 Journey Inside The Atom

Access targeted multiple-choice questions for Chapter 08 Journey Inside The Atom designed to align with the latest CBSE academic syllabus for Class 9 Science. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Download Chapter 08 Journey Inside The Atom MCQs with Answers

Access the complete set of multiple-choice questions for Chapter 08 Journey Inside The Atom below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official CBSE textbooks.

Question: In ancient India, Acharya Kanada proposed that repeatedly dividing matter would eventually reveal particles too small to be divided any further. What Sanskrit term did he use to describe these ultimate constituents of matter?
A. Dravya
B. Parmanu
C. Atom
D. Nucleon
Show Answer & Explanation

Answer: (B) Parmanu

Explanation:
The chapter explicitly states that Acharya Kanada called these smallest indivisible particles 'parmanus' and recorded his ideas in the Vaisesika Sutras. The term dravya referred to matter itself in his framework, not the particles.

Question: J. J. Thomson's experiments with cathode rays revealed that the nature of the rays was independent of both the cathode material and the gas inside the tube. What significance did this finding have for atomic theory?
A. It proved that atoms contain only electrons
B. It showed that electrons are a fundamental component present in all atoms of every element
C. It demonstrated that cathode rays originate from the nucleus
D. It established that atoms are completely divisible into smaller parts
Show Answer & Explanation

Answer: (B) It showed that electrons are a fundamental component present in all atoms of every element

Explanation:
The chapter notes that because the cathode ray behaviour was constant regardless of cathode material or gas type, scientists concluded that electrons must be a universal component of all atoms. This uniformity across different elements was the key insight.

Question: According to Rutherford's interpretation of his gold foil experiment results, the fact that most alpha particles passed through the foil without deflection suggests what feature of atomic structure?
A. Atoms are solid, dense spheres throughout
B. Atoms consist mostly of empty space
C. The nucleus is located on the outer edge of the atom
D. Electrons form a protective barrier around the nucleus
Show Answer & Explanation

Answer: (B) Atoms consist mostly of empty space

Explanation:
Rutherford concluded from the undeflected passage of most particles that atoms are largely empty space. If atoms were solid throughout, far more particles would have encountered obstruction.

Question: Rutherford discovered that the nucleus is extremely small relative to the atom itself. To illustrate this scale difference, the chapter uses a specific analogy. If an atom were the size of a cricket ground, what would the nucleus resemble?
A. A grain of sand
B. A tiny black pepper grain just a few mm across
C. A marble
D. A tennis ball
Show Answer & Explanation

Answer: (B) A tiny black pepper grain just a few mm across

Explanation:
The chapter provides this exact comparison: if an atom were about 100 metres across (cricket ground size), the nucleus would be roughly the size of a tiny black pepper grain, only a few millimetres in diameter.

Question: When Bohr introduced his model of the atom, he proposed that electrons occupy fixed circular paths called stationary states or shells. What was the primary problem with Rutherford's model that Bohr's concept of stationary states solved?
A. Rutherford could not explain why atoms have a nucleus
B. Rutherford's model predicted atoms should collapse because orbiting electrons should lose energy and spiral into the nucleus
C. Rutherford claimed electrons move randomly rather than in paths
D. Rutherford believed electrons were located inside the nucleus
Show Answer & Explanation

Answer: (B) Rutherford's model predicted atoms should collapse because orbiting electrons should lose energy and spiral into the nucleus

Explanation:
• Rutherford's circular-orbit model created a physics problem: accelerating charged particles should radiate energy
• This energy loss would cause electrons to spiral inward
• Atoms would collapse—but clearly they don't
• Bohr solved this by proposing electrons in stationary states don't lose energy while orbiting

Question: James Chadwick's discovery of the neutron in 1932 resolved a longstanding puzzle about atomic mass. What was the specific problem that his discovery explained?
A. Why atoms have different numbers of electrons than protons
B. Why a helium atom with only two protons had a mass approximately four times that of hydrogen, not double
C. Why the nucleus contains both positive and negative charges
D. Why electrons are found outside the nucleus rather than inside it
Show Answer & Explanation

Answer: (B) Why a helium atom with only two protons had a mass approximately four times that of hydrogen, not double

Explanation:
Helium has two protons like hydrogen has one, yet helium's mass is roughly four times that of hydrogen. Neutrons, with mass nearly equal to protons but no charge, accounted for this 'missing' mass. The chapter explicitly describes this as the puzzle Chadwick solved.

Question: The chapter explains that in writing chemical symbols according to IUPAC rules, the first letter of a symbol is always written in uppercase while any second letter is lowercase. Which of these correctly follows this convention?
A. CO (for cobalt)
B. co (for cobalt)
C. Co (for cobalt)
D. cO (for cobalt)
Show Answer & Explanation

Answer: (C) Co (for cobalt)

Explanation:
The chapter clearly states that the first letter is capital (uppercase) and the second letter, if present, is small (lowercase). For cobalt, the correct symbol is Co, not CO, co, or cO.

Question: An atom has 17 protons and 20 neutrons. Based solely on this information, how many electrons must this neutral atom have?
A. 20 electrons
B. 37 electrons
C. 17 electrons
D. 3 electrons
Show Answer & Explanation

Answer: (C) 17 electrons

Explanation:
For an atom to be electrically neutral, the number of electrons must equal the number of protons. Since the atom has 17 protons, it must have 17 electrons. The number of neutrons does not affect electron count in a neutral atom.

Question: The chapter introduces the concept of the valence shell and valence electrons. For an atom with electronic configuration 2, 8, 5, which shell is the valence shell and how many valence electrons are present?
A. K-shell with 2 valence electrons
B. L-shell with 8 valence electrons
C. M-shell with 5 valence electrons
D. N-shell with 5 valence electrons
Show Answer & Explanation

Answer: (C) M-shell with 5 valence electrons

Explanation:
The valence shell is the outermost shell containing electrons. For configuration 2, 8, 5, the M-shell (third shell) is the outermost and contains 5 electrons. These 5 valence electrons determine the atom's combining capacity.

Question: Two atoms have the same number of protons but different numbers of neutrons, resulting in different mass numbers. What term does the chapter use to describe this relationship between the two atoms?
A. Isobars
B. Isotopes
C. Isomers
D. Ions
Show Answer & Explanation

Answer: (B) Isotopes

Explanation:
Isotopes are defined in the chapter as atoms of the same element (same atomic number and same number of protons) that have different numbers of neutrons and therefore different mass numbers. Isobars, by contrast, have the same mass number but different atomic numbers.

Question: The chapter describes how chlorine's average atomic mass is 35.5 u rather than simply 36 u. The 35.5 figure is obtained by considering that one isotope (³⁵Cl) makes up about 75% while the other (³⁷Cl) makes up about 25% of natural chlorine. What type of average is 35.5 u called?
A. Simple arithmetic mean
B. Weighted average atomic mass
C. Median atomic mass
D. Mode atomic mass
Show Answer & Explanation

Answer: (B) Weighted average atomic mass

Explanation:
The chapter explicitly distinguishes between a simple average (which ignores the relative abundances of isotopes) and a weighted average atomic mass, which multiplies each isotope's mass by its percent relative abundance. The 35.5 u value is the weighted average, which accurately reflects how chlorine occurs in nature.

Question: When alpha particles were directed at the gold foil in Rutherford's experiment, according to Thomson's plum pudding model, what outcome was expected?
A. Most particles would bounce straight back because the foil is solid
B. Alpha particles would pass straight through with little or no deflection because positive charge is spread evenly throughout
C. All particles would be stopped by the foil
D. Particles would be deflected by electrons embedded in the positive sphere
Show Answer & Explanation

Answer: (B) Alpha particles would pass straight through with little or no deflection because positive charge is spread evenly throughout

Explanation:
Thomson's model spread positive charge uniformly throughout the atom. If true, alpha particles (being positively charged) would experience only weak, even resistance and should pass through nearly straight. The actual result—some sharp deflections and a few bouncebacks—contradicted this expectation.

Question: The chapter notes that even though Bohr's model successfully explained why atoms are stable, it was eventually found to have limitations. According to the text, what was the next major development in atomic modelling that superseded Bohr's approach?
A. The plum pudding model was reinstated
B. The quantum mechanical model was proposed
C. Thomson's model was refined
D. A return to Dalton's indivisible atom idea
Show Answer & Explanation

Answer: (B) The quantum mechanical model was proposed

Explanation:
The chapter's 'Next Level Up' box explicitly states that later, even Bohr's model was found to have limitations and another model, the quantum mechanical model, was proposed, which students would learn about in higher grades.

Question: Acharya Kanada and the Greek philosophers Leucippus and Democritus lived in very different times and places, yet both independently proposed the existence of tiny indivisible particles. Which fundamental question about the natural world drove both civilisations to this same line of thinking?
A. How do atoms combine to form compounds?
B. What is the source of energy in living organisms?
C. What is everything in the universe made up of?
D. Why do some materials conduct electricity while others do not?
Show Answer & Explanation

Answer: (C) What is everything in the universe made up of?

Explanation:
The chapter begins by noting that both ancient Indian and Greek thinkers pondered the same fundamental question across centuries: 'What is everything made up of?' This shared curiosity drove them independently to propose the concept of indivisible particles, though they had no experimental evidence.

Question: In the standard atomic notation such as ¹²₆C shown in the chapter, the mass number 12 is written above and to the left of the symbol, while the atomic number 6 is written below. Which of these numbers directly determines the identity of the element?
A. The mass number, because it indicates total nucleons
B. The atomic number, because it indicates the number of protons
C. Both are equally important for identifying the element
D. Neither number uniquely identifies the element
Show Answer & Explanation

Answer: (B) The atomic number, because it indicates the number of protons

Explanation:
The chapter states explicitly that atomic number 'determines the identity of an element and its chemical behaviour.' While mass number can vary (isotopes), atomic number is unique to each element and is what truly defines what element an atom is.

Question: Acharya Kanada proposed that repeatedly dividing matter would eventually yield particles that cannot be separated further. In his framework recorded in the Vaisesika Sutras, what name did he assign to these ultimate, indivisible units?
A. atomos
B. parmanu
C. nucleons
D. dyads
Show Answer & Explanation

Answer: (B) parmanu

Explanation:
Acharya Kanada called the smallest indivisible particles parmanus. His ideas, documented in the Vaisesika Sutras, described how repeated division of matter leads to these infinitely small particles that form dyads and triads, which then combine to create the material universe.

Question: J. J. Thomson observed cathode rays in his 1897 experiments and concluded they consisted of negatively charged particles. What key finding about these particles suggested they were fundamental components of all atoms?
A. The rays could only be produced from specific metals
B. The nature of the rays was independent of the cathode material and the gas in the tube
C. The rays carried a positive charge when measured in a magnetic field
D. The rays could penetrate through solid barriers without any deflection
Show Answer & Explanation

Answer: (B) The nature of the rays was independent of the cathode material and the gas in the tube

Explanation:
Thomson found that cathode rays exhibited the same properties regardless of which metal formed the cathode or which gas filled the tube, demonstrating that these negatively charged particles were a universal component present in every element, not unique to any particular substance.

Question: During Rutherford's gold foil experiment, while most alpha particles passed straight through without deflection, a few bounced sharply backward. What critical conclusion did Rutherford draw from these rare backward-bouncing particles?
A. The nucleus contained only electrons and neutrons
B. The positive charge and most of the atom's mass were concentrated in an extremely small region at the centre
C. The gold foil was thicker than expected and absorbed most particles
D. Electrons were arranged in fixed orbits around a central point
Show Answer & Explanation

Answer: (B) The positive charge and most of the atom's mass were concentrated in an extremely small region at the centre

Explanation:
The backward-bouncing alpha particles indicated they had collided with something very dense and strongly positively charged. This could only occur if the atom's positive charge and mass were tightly packed into a tiny central nucleus rather than spread throughout, as Thomson's model had suggested.

Question: Why did Rutherford's planetary model of the atom face a fundamental stability problem that Bohr's model later addressed?
A. Electrons moving in circular orbits would continuously emit energy and spiral into the nucleus, causing the atom to collapse
B. The nucleus did not contain enough protons to balance the negative charge of orbiting electrons
C. Alpha particles would interfere with the electron orbits and disrupt the atom's structure
D. The nucleus itself was too unstable and would spontaneously break apart
Show Answer & Explanation

Answer: (A) Electrons moving in circular orbits would continuously emit energy and spiral into the nucleus, causing the atom to collapse

Explanation:
In a circular orbit, an accelerating charged particle loses energy and should spiral inward. Rutherford's model could not explain why electrons, attracted to the positive nucleus and constantly changing direction as they orbited, did not simply lose energy and collapse into the nucleus, destroying the atom's stability.

Question: James Chadwick discovered a subatomic particle in 1932 that possessed nearly equal mass to a proton but carried no electrical charge. What puzzle in atomic physics did this discovery finally resolve?
A. Why some atoms were radioactive and others were not
B. Why helium atoms were roughly four times heavier than hydrogen atoms despite having only twice as many protons
C. Why electrons did not fall into the nucleus due to electrostatic attraction
D. Why different elements had different numbers of electron shells
Show Answer & Explanation

Answer: (B) Why helium atoms were roughly four times heavier than hydrogen atoms despite having only twice as many protons

Explanation:
• Hydrogen has 1 proton but helium has 2 protons
• Yet helium's mass is about 4 times greater, not just 2 times
• Chadwick's neutrons—with mass similar to protons but zero charge—explained where the extra mass came from without adding to the nuclear charge.

Question: In Bohr's model, electrons occupy fixed energy levels represented by the letters K, L, M, N and so on. According to the chapter's 'Threads of Curiosity' section, why were these particular letters chosen for naming the shells rather than starting with A, B, C, D?
A. K stood for 'kernel,' the German word for nucleus
B. Early X-ray experiments by Charles Barkla used K as the first letter, with space deliberately left for any earlier series that might be discovered
C. John Dalton had already assigned A, B, C to represent different states of matter
D. Niels Bohr preferred the alphabetic sequence starting from the middle of the alphabet
Show Answer & Explanation

Answer: (B) Early X-ray experiments by Charles Barkla used K as the first letter, with space deliberately left for any earlier series that might be discovered

Explanation:
Charles Barkla's early X-ray studies labeled the first observed line as K, intentionally skipping A through J in case an earlier series were found. Though no earlier series was ever discovered, Bohr adopted this same notation when naming atomic shells, and it has remained the standard since.

Question: According to the rules described in the chapter for electron distribution in shells, the maximum number of electrons that the L-shell (second shell) can accommodate is determined by which formula?
A. 2n where n = 2
B. 2n² where n = 2
C. n² + 1 where n = 2
D. 2n + 2 where n = 2
Show Answer & Explanation

Answer: (B) 2n² where n = 2

Explanation:
The formula 2n² governs maximum electrons per shell, where n is the shell number. For the L-shell, n = 2, so 2(2)² = 8 electrons maximum. The K-shell (n = 1) holds 2(1)² = 2 electrons, and the M-shell (n = 3) holds 2(3)² = 18 electrons.

Question: An atom with 17 protons and 18 neutrons remains electrically neutral. Based on this information, what is its atomic number and how many electrons does it contain?
A. Atomic number 18, with 17 electrons
B. Atomic number 17, with 17 electrons
C. Atomic number 35, with 18 electrons
D. Atomic number 17, with 18 electrons
Show Answer & Explanation

Answer: (B) Atomic number 17, with 17 electrons

Explanation:
Atomic number equals the number of protons, which is 17 for this atom. Since a neutral atom must have equal protons and electrons to balance charge, it contains 17 electrons. The neutron count does not affect the atomic number or electron count.

Question: Carbon has three naturally occurring isotopes: ¹²C, ¹³C, and ¹⁴C. Despite differing in the number of neutrons they contain, these isotopes display essentially identical chemical behaviour. What is the reason for their similar chemical properties?
A. They all exist as solid materials at room temperature
B. They have the same number of electrons and the same electronic configuration, so valence electron behaviour is identical
C. Neutrons dominate chemical bonding more than electrons do
D. The difference in mass between isotopes causes their reactivity to be uniform
Show Answer & Explanation

Answer: (B) They have the same number of electrons and the same electronic configuration, so valence electron behaviour is identical

Explanation:
All three carbon isotopes have 6 protons and 6 electrons, giving them the same electronic configuration with 4 valence electrons. Since chemical properties depend on valence electrons, not neutrons, isotopes are chemically nearly identical despite different mass numbers.

Question: Two different elements—calcium with 20 protons, potassium with 19 protons, and argon with 18 protons—each have a mass number of 40. What term does the chapter use to describe atoms of different elements that share the same mass number but different atomic numbers?
A. Isotopes
B. Allotropes
C. Isobars
D. Nucleons
Show Answer & Explanation

Answer: (C) Isobars

Explanation:
Isobars are atoms of different elements possessing the same mass number but different atomic numbers. In contrast, isotopes are atoms of the same element with different mass numbers. Calcium-40, potassium-40, and argon-40 are three distinct isobars that all contain 40 total nucleons.

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